Cutting balloon with connector and dilation element

ABSTRACT

A balloon catheter is provided that may be used to dilate hardened regions of a stenosis. The balloon catheter is provided with one or more dilation elements that extend along a surface of a balloon. Each dilation element is monolithically connected to an outer surface of the balloon by a connector. The connector is sufficiently sized and designed to undergo stress-induced plastic deformation incurred during blow molding so that a significant portion of each of the dilation elements does not become absorbed into the wall of the final blow molded balloon, thereby maintaining the structural integrity of each of the dilation elements. The dilation element has a flattened outer surface along at least proximal and distal neck portions of the balloon.

BACKGROUND

The present invention relates generally to medical devices and moreparticularly to balloon catheters used to dilate narrowed portions of alumen.

Balloon catheters are widely used in the medical profession for variousintraluminal procedures. One common procedure involving the use of aballoon catheter relates to angioplasty dilation of coronary or otherarteries suffering from stenosis (i.e., a narrowing of the arteriallumen that restricts blood flow).

Although balloon catheters are used in many other procedures as well,coronary angioplasty using a balloon catheter has drawn particularattention from the medical community because of the growing number ofpeople suffering from heart problems associated with stenosis. This hasled to an increased demand for medical procedures to treat suchproblems. The widespread frequency of heart problems may be due to anumber of societal changes, including the tendency of people to exerciseless while eating greater quantities of unhealthy foods, in conjunctionwith the fact that people generally now have longer life spans thanprevious generations. Angioplasty procedures have become a popularalternative for treating coronary stenosis because angioplastyprocedures are considerably less invasive than other alternatives. Forexample, stenosis of the coronary arteries has traditionally beentreated with bypass surgery. In general, bypass surgery involvessplitting the chest bone to open the chest cavity and grafting areplacement vessel onto the heart to bypass the blocked, or stenosed,artery. However, coronary bypass surgery is a very invasive procedurethat is risky and requires a long recovery time for the patient.

To address the increased need for coronary artery treatments, themedical community has turned to angioplasty procedures, in combinationwith stenting procedures, to avoid the problems associated withtraditional bypass surgery. Typically, angioplasty procedures areperformed using a balloon-tipped catheter that may or may not have astent mounted on the balloon (also referred to as a stented catheter).The physician performs the angioplasty procedure by introducing theballoon catheter into a peripheral artery (commonly one of the legarteries) and threading the catheter to the narrowed part of thecoronary artery to be treated. During this stage, the balloon isuninflated and collapsed onto the shaft of the catheter in order topresent a low profile which may be passed through the arterial lumens.Once the balloon is positioned at the narrowed part of the artery, theballoon is expanded by pumping a mixture of saline and contrast solutionthrough the catheter to the balloon. As a result, the balloon pressesagainst the inner wall of the artery to dilate it. If a stent is mountedon the balloon, the balloon inflation also serves to expand the stentand implant it within the artery. After the artery is dilated, theballoon is deflated so that it once again collapses onto the shaft ofthe catheter. The balloon-tipped catheter is then retracted from thebody. If a stent is mounted on the balloon of the catheter, the stent isleft permanently implanted in its expanded state at the desired locationin the artery to provide a support structure that prevents the arteryfrom collapsing back to its pre-dilated condition. On the other hand, ifthe balloon catheter is not adapted for delivery of a stent, either aballoon-expandable stent or a self-expandable stent may be implanted inthe dilated region in a follow-up procedure. Although the treatment ofstenosed coronary arteries is one common example where balloon cathetershave been used, this is only one example of how balloon catheters may beused and many other uses are also possible.

One problem that may be encountered with conventional angioplastytechniques is the proper dilation of stenosed regions that are hardenedand/or have become calcified. Stenosed regions may become hardened for avariety of reasons, such as the buildup of atherosclerotic plaque orother substances. Hardened regions of stenosis can be difficult tocompletely dilate using conventional balloons because hardened regionstend to resist the expansion pressures applied by conventional ballooncatheters. Although the inventions described below may be useful intreating hardened regions of stenosis, the claimed inventions may alsosolve other problems as well.

SUMMARY

The invention may include any of the following aspects in variouscombinations and may also include any other aspect described below inthe written description or in the attached drawings.

In a first aspect, a method of forming a balloon is provided. A blowmold parison is provided comprising a substantially cylindrical bodyportion, the body portion comprising an outer wall and an inner wall,the body portion further comprising an aperture extending along acentral axis of the body portion; an extension element projecting awayfrom the outer wall, the extension element comprising a first height anda first effective width; and a structural feature projecting away fromthe outer wall of the body portion, the structural feature beingintegrally molded to the extension element, the structural featurecomprising a second effective width greater than the first effectivewidth of the extension element. The blow parison is inserted into aforming mold. A predetermined amount of heat and pressure is applied tothe parison. The parison is stretched in a longitudinal direction. Theparison is expanded in a radial direction, wherein the extension elementundergoes stress-induced plastic deformation developed during the radialexpansion to maintain the structural integrity of the structuralfeature.

In a second aspect, a balloon catheter for dilation of a vessel wall isprovided. The balloon catheter comprises a balloon having a distalportion, and a proximal portion, wherein at least a length of an outersurface of the balloon comprises a working diameter adapted to dilatethe vessel wall; a shaft having a distal end and a proximal end, theballoon being mounted on the distal end of the shaft, wherein the shaftfurther comprises an inflation lumen extending therethrough in fluidcommunication with an interior region of the balloon, the balloonthereby being expandable between a deflated state and an inflated state;and a protuberance disposed along the outer surface of the balloon, theprotuberance being affixed to the outer surface of the balloon at aninterface region, the protuberance comprising a dilation element and aconnector, the dilation element extending away from the outer surface ofthe balloon and being characterized by a second effective width, theconnector connecting the dilation element to the outer surface of theballoon at the interface, the connector characterized by a firsteffective width less than the second effective width of the protrusion.

In a third aspect, a blow mold parison for a balloon is provided. Theparison comprises a substantially cylindrical body portion, the bodyportion comprising an outer wall and an inner wall, the body portionfurther comprising an aperture extending along a central axis of thebody portion; an extension element extending from the outer wall of thebody portion, the extension element projecting away from the outer wall,the extension element comprising a first height and a first effectivewidth; and a structural feature projecting from the outer wall of thebody portion, the structural feature being integrally molded to theextension element, the structural feature comprising a second effectivewidth greater than the first effective width of the extension element.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The invention may be more fully understood by reading the followingdescription in conjunction with the drawings, in which:

FIG. 1 is a cross-sectional view of a balloon including a dilationelement connected to an outer surface of the balloon by a connector;

FIG. 2 shows a perspective view of the balloon of FIG. 1 with theballoon mounted on a shaft;

FIG. 3 shows a parison precursor to the final balloon of FIGS. 1 and 2;

FIG. 4 shows a blown-up cross-sectional view of FIG. 3 and shows thestructural feature and extension element integrally molded into theouter wall of the body portion;

FIG. 5 shows a blown-up cross-sectional view of FIG. 3 in which theparison is unstretched in the longitudinal and radial directions;

FIGS. 6-8 show possible design configurations of the structural featureand extension element;

FIG. 9 shows the parison of FIG. 3 placed within a forming mold;

FIG. 10 shows the parison of FIG. 9 longitudinally stretched;

FIG. 11 shows the parison of FIG. 10 about to be radially expanded;

FIGS. 12-13 show the final blow molded balloon structure;

FIG. 14 shows another final blow molded balloon structure;

FIG. 15 shows a protective jacket which may be placed over a structuralfeature of the parison before blow molding the parison;

FIG. 16 shows a blown up view of a longitudinally stretched parison;

FIG. 17 shows a perspective view of the protective jacket of FIG. 15;

FIG. 18 shows a longitudinal cross-sectional view of the jacket disposedover the parison;

FIG. 19 shows the balloon in a deflated state having a foldedarrangement with the dilation element and connector disposed along thetop of the folds; and

FIG. 20 shows a block diagram of a coextrusion process for forming aballoon from a first polymeric material and an extension element from ablend of the first and a second polymeric material, and a structuralfeature from the second polymeric material.

DETAILED DESCRIPTION

As used herein, the term “extension element” refers to a slender portionthat connects a structural feature to the outer wall of a parison. The“extension element” becomes a “connector” of a balloon after a blowmolding process. The term “structural feature” refers to that portion ofthe parison that becomes a “dilation element” of the balloon after theblow molding process.

FIG. 1 shows a cross-sectional view of a balloon 150 comprising apreferred design configuration of protuberances 110 disposed along anouter surface 140 of the balloon 150. The protuberances 110 are shown tobe integral with the outer surface 140 of the balloon 150. Each of theprotuberances 110 comprises a dilation element 130 and a connector 120.The connector 120 is preferably integrated into the outer surface 140 ofthe balloon 150. During the blow molding process used to form theballoon 150, the connector 120 is sufficiently sized such that a portionof the connector or all of the connector 120 is absorbed into the wallof the balloon 150 to maintain the structural integrity of the dilationelement 130, as will be explained in detail below. During inflation ofthe balloon 150, the force exerted by the inflated balloon 150 may befocused to the dilation elements 130 and thereafter transferred throughthe dilation elements 130 to a stenosed vessel wall. The concentratedforce exerted by the dilation elements 130 against the stenosed regionis sufficient to fracture plaque from the vessel wall.

FIG. 2 shows the balloon 150 connected to a shaft 170. The outer surface140 of the balloon 150 has a working diameter 190 that extends alongpart of the length of the balloon 150. The length W d of the workingdiameter may be defined as the distance between the balloon proximalend, where the tapered proximal portion meets the working diameter 190and the balloon distal end, where the tapered distal portion meets theworking diameter 190. The working diameter 190 of the balloon 150 may beconnected to the shaft 170 with the tapered proximal portion and thetapered distal portion of the balloon 150. Typically, the workingdiameter 190 of the balloon 150 is a portion that inflates to agenerally uniform circumference in order to evenly dilate a section of alumen. However, the working diameter 190 does not necessarily need tohave a uniform circumference.

Still referring to FIG. 2, the protuberances 110 are shown tocontinuously extend in the longitudinal direction along the workingdiameter 190 of the balloon 150 and the tapered proximal and distalportions of the balloon 150. The protuberances 110 are oriented about acircumference of the outer surface 140 of the balloon 150 and are showncircumferentially spaced apart from each other about the outer surface140 of the balloon 150. Other configurations of the protuberances 110about the outer surface 140 of the balloon 150 are contemplated. Forexample, the protuberances 110 may be configured in a spiral arrangementabout the balloon 150 or extend only about the working diameter 190 ofthe balloon 150.

Alternatively, the protuberances 110 may extend along at least a portionof the proximal neck and/or distal neck of the balloon 150 where theballoon 150 is bonded to the shaft 170. In one embodiment, at least aportion of the protuberances 110 that extend along the neck of theballoon 150 is heat bonded to the shaft 170. In particular, the overalldimensions of the protuberances 110 may gradually increase from the heatbonded region to the working diameter 190 of the balloon 150. Such atransitioning in the bead size may assist with the refolding of theballoon 150 into a pleated configuration (discussed in greater detailbelow in conjunction with FIG. 19). Additionally, the transitioning mayfacilitate insertion and withdrawal of the balloon 150 from an outerdelivery sheath that is commonly utilized during the angioplastyprocedure.

The number of protuberances 110 oriented about the balloon 150 may alsovary. The exact number of protuberances 110 is dependent upon a numberof factors, including, but not limited to, the type of stenosed regioninto which the balloon 150 is inserted. In a preferred embodiment, theballoon 150 has three or four protuberances 110, the exact number beingdependent to a degree upon the balloon profile that is suitable for aparticular application.

Forming the final shape of the balloon 150 typically involves a blowmolding process. FIG. 3 shows a parison 300, which is the precursorstructure to the final shaped balloon 150 shown in FIGS. 1 and 2. Theterm “parison” as used herein refers to the raw balloon tubing prior toblow molding the final balloon 150 structure. Generally speaking, blowmolding of the parison 300 transforms the parison 300 into the finalshaped balloon 150. Preferably, the parison 300 is formed from a screwextrusion process as is known to one of ordinary skill in the art. Theparison 300 comprises a cylindrical body portion 310. The body portion310 includes an outer wall 311 and an inner wall 312. An aperture 313extends through the central axis of the body portion 310. The aperture313 becomes the inflation lumen of the balloon 150 after blow molding.The parison 310 further includes a structural feature 320 which projectsaway from the outer wall 311 of the body portion 310. The structuralfeature 320 becomes the dilation element 130 after the blow moldingprocess. An extension element 330 connects the structural feature 320 tothe outer wall 311 of the body portion 310. The extension element 330becomes the connector 120 after the blow molding process. The extensionelement 330 is preferably integrally molded into the outer wall 311 ofthe body portion 310.

FIG. 4 is a blown up cross-sectional view of FIG. 3 and shows thestructural feature 320 and extension element 330 integrally molded intothe outer wall 311 of the body portion 310. As will be explained, theextension element 330 is designed to prevent significant absorption ofthe structural feature 320 into the wall of the cylindrical body portion310 of the parison 300 during the blow molding process, therebymaintaining the structural integrity of the dilation element 130 of theballoon 150.

FIG. 5 shows another blown up cross-sectional view of FIG. 3. FIG. 5represents the parison 300 prior to being longitudinally and radiallystretched during the blow molding process. Extension element 330 isshown to have a first effective width Wee. The first effective width Weeas used herein means the largest lateral dimension of the extensionelement 330. FIG. 5 indicates that the largest lateral dimension of theextension element 330 is situated close to the outer wall 311 of bodyportion 310. The largest lateral dimension of the extension element 330may be situated anywhere else along the extension element 330. Theextension element 330 may also be characterized by a height, Hee. Theheight Hee spans from the base 316 of the outer wall 311 to the base 317of the structural feature 320. The base 316 may be designed with apredetermined radius of curvature to alleviate the stress incurredduring blow molding, thereby facilitating absorption of the extensionelement 330 into the wall of the body portion 310.

FIG. 5 shows that the structural feature 320 has a second effectivewidth, Wsf. The second effective width Wsf as used herein means thelargest lateral dimension of the structural feature 320. FIG. 5indicates that the largest lateral dimension of the structural feature320 is the diameter. Various dimensions are contemplated for the firsteffective width W_(ee), the second effective width W_(sf), and theheight H_(ee) of the extension element 330. However, the parison 300 ispreferably designed such that the second effective width W_(sf) isgreater than the first effective width W_(ee) to preserve the structuralintegrity of the dilation element 130 after blow molding.

Other design configurations for the first effective width Wee and thesecond effective width W_(sf) are contemplated. For example, the firsteffective width W_(ee) may be substantially equal to the secondeffective width W_(sf) such that the extension 330 is characterized bythe absence of a necked-down region. Alternatively, the first effectivewidth W_(ee) may be larger than the second effective width W_(sf).

Although FIG. 5 shows that the structural feature 320 is bead-shaped,other shapes for the structural feature and extension element of theparison are contemplated, as shown in FIGS. 6-8. For example, FIG. 6shows that the structural feature includes a bead-like structure 600which is asymmetrical about a central radial plane 610 through extensionelement 620. Each of the bead-like structures 600 includes extensionelements 620 which connect the body portion 310 to the asymmetricalbead-like structure 600. The extension elements 620 are shown to besubstantially perpendicular to the outer wall 311 of the body portion310. A radius of curvature may exist at the region at which theextension elements 620 contacts the outer wall 311. The radius ofcurvature may help to lower the stresses and strains incurred during theradial expansion process of the blow molding process. FIG. 6 shows thatthe effective width W_(ee) of each of the extension elements 620 is lessthan the effective width W_(sf) of each of the structural features 600.

FIGS. 7a and 7b show another possible design configuration of thestructural feature and extension element about the body portion 310.FIGS. 7a and 7b shows a tapered structural feature 750 having a firstedge 720 and a second edge 710. Both edges 710 and 720 taper inwardlytowards each other in the radial direction until they terminate atpointed edge 730. Such a tapered structural feature 750 possesses asmaller cross-sectional area at pointed edge 730 which contacts thevessel wall, thereby enabling the force transmitted from the structuralfeature 730 to the vessel wall to be more focused. The extension element740 is shown to have curved edges 741 and 742 which connect the bodyportion 310 to the base 745 of the tapered structural feature 750. FIGS.7a and 7b show that the effective width Wee of the extension element 740is less than the effective width Wsf of the structural feature 750.

FIG. 8 shows yet another possible design configuration of the structuralfeature and extension element. FIG. 8 shows a crown-shaped structuralfeature 800 connected to outer wall 311 of body portion 310 by extensionelement 810. The extension elements 810 are shown to be substantiallyperpendicular to the outer wall 311 of the body portion 310. FIG. 8shows that the effective width W_(ee) of each of the extension elements810 is less than the effective width W_(sf) of each of the structuralfeatures 800.

Various dimensions of the structural feature 320 and extension element330 (referring for convenience to FIGS. 3-5) are contemplated. Forexample, the height H_(ee) of the extension element 330 may be greaterthan the effective width W_(sf) of the structural feature 320. Theparticular type of design configuration of the structural feature andextension element may be dependent upon numerous factors, including inpart the ease of reproducibility of the parison 300 and balloon 150during manufacturing. Additionally, the height H_(ee) and effectivewidth W_(ee) of extension element 330 should be sufficient to preventsignificant absorption of the structural feature 320 into the wall ofthe parison 300 during blow molding.

Additionally, the parison 300 may be designed to have variousconfigurations of the extension element 330 and structural feature 320.Preferably, the extension element 330 and structural feature 320 areconfigured longitudinally (FIG. 2) along the outer surface of theparison 300. Alternatively, the extension element 330 and structuralfeature 320 may spirally extend along the outer surface of the parison300. Alternatively, the extension element 330 and structural feature 320may extend only along a finite distance of the parison 300. The parison300 may also comprise a series of discrete extension elements 330 andstructural features 320. The specific configuration of the extensionelement 330 and structural feature 320 about the parison 300 may bedependent upon numerous factors, including the geometry of the stenosedvessel and the particular application.

FIGS. 3-8 represent examples of the type of parisons which may be usedfor blow molding a balloon into its final shape. The blow moldingprocess forms the final shape and properties of the balloon 150. Afterselecting the desired shapes and dimensions of the structural feature320 and extension element 330 (FIG. 3), the parison 300 is placed into aforming mold 900 as shown in FIG. 9. Suitable heat and pressure as knownin the art are applied to the parison 300. Thereafter, the parison 500is stretched in the longitudinal direction as shown in FIG. 10. Thelongitudinal stretch of the parison 500 decreases the overallcross-sectional area of the parison 300 such that the wall thickness ofthe parison 300, the effective width W_(ee) of extension element 330,and the effective width W_(sf) of the structural features 320 havedecreased dimensions. These overall dimensions of the parison 500decrease as the parison 500 is being stretched longitudinally. A typicallongitudinal stretch of the parison 300 can be from about 2 times toabout 4 times the initial inner diameter of the parison 300. FIG. 16shows the parison 500 after it has been longitudinally stretched. FIG.16 shows that the effective width W_(ee) of the extension element 520has decreased relative to the unstretched longitudinal parison 300 ofFIG. 5. Accordingly, the height of the extension element 520 has alsodecreased. Although the effective width W_(SF) of the structural feature530 has also decreased during the longitudinal stretch of the parison300, the structural integrity of the feature 530 is shown to remainintact. In the example shown in FIGS. 5 and 16, the structural feature530 still retains a bead-like structure.

After the parison 300 has been stretched in the longitudinal directionto form the parison 500 of FIG. 5, radial expansion of the parison 500may occur. FIG. 11 shows that the longitudinally stretched parison 500radially expands upon applying suitable heat and pressure to the parison500 as known in the art. The parison 500 radially expands towards thewalls 901 and 902 of the mold 900 as indicated by the vertical arrows inFIG. 11. The radial expansion as shown in FIG. 11 gives thelongitudinally stretched parison 500 the required radial strength andshape. Radial expansion may be achieved by capping off one of the endsof the parison 500 and then introducing hot pressurized gas orpressurized air into the open uncapped end, thereby causing the parison500 to expand and conform to the shape of the forming mold 900. Theparison 500 may typically expand from about 5 times to about 6 times theinitial inner diameter of the parison 300 of FIG. 3. During the radialexpansion, the wall thickness of the parison 500 decreases from theradial expansion. The extension element 520 (FIG. 16) undergoesstress-induced plastic deformation during radial expansion and a portionof it becomes part of the wall of the parison 500. The height andeffective width of the extension element 520 decreases in the process ofbecoming part of the wall of the parison 500. However, the shape of thestructural feature 530 remains substantially intact during radialexpansion of the structural feature 530 (FIG. 16). Preferably, theextension element 530 is designed with sufficient material to undergostress-induced plastic deformation during the radial expansion withoutaffecting the structural integrity of the structural feature 530.

The resultant balloon after longitudinal stretching and radial expansionis shown in FIGS. 12-14. FIGS. 12 and 13 show an example of a resultantballoon 1200 formed after blow molding of the parison 300 (FIG. 3). FIG.12 shows a cross sectional view of the final blow molded balloon 1200.Dilation element 1205 extends radially away from the outer surface 1220of the balloon 1200. The dilation element 1205 includes rounded edges1207 and 1208 and flattened edges 1206 and 1209. Formation of flattenededge 1206 may occur as the bead-like structural feature 530 (FIG. 12)radially expands and contacts the smooth wall 901 of mold 900. Connector1210 connects flattened edge 1209 to outer surface 1220 of balloon 1200.

FIG. 13 shows an expanded view of FIG. 12. In particular, FIG. 13 showsthat connector 1210 connects flattened edge 1209 to outer surface 1220of balloon 1200 at an interface region 1250 where the connector 1210contacts the outer surface 1220 of the balloon 1200. The interface 1250region is characterized by a wall thickness greater than a wallthickness of a noninterface region, such as that shown at 1280 in FIG.12. This greater wall thickness at the interface 1250 is attributed tothe connector 1210 being absorbed in the wall of the balloon 1200 at theinterface region 1250 during blow molding. The extension element 330 ofthe parison 300 (FIGS. 3 and 4) is preferably designed with suitableheight Hee and effective width Wee dimensions such that the resultantconnector 1210 possesses sufficient material from which the wall of theballoon 1200 can absorb thereinto without disturbing the shape andstructural integrity of the dilation element 1205. FIGS. 12 and 13 showthat the effective width of the connector 1210 remains less than theeffective width of the dilation element 1205.

Although the dilation element 1205 is shown radially oriented withrespect to the outer surface 1220 of the balloon 1200, numerous otherconfigurations of the resultant dilation element 1205 are contemplated.For example, the dilation element 1205 may be inclined relative theouter surface 1220 of the balloon 1200, as shown in FIG. 14. Such aconfiguration may be formed during radial expansion (FIG. 11), in whichthe structural feature 530 (FIG. 16) becomes inclined after contactingthe wall 901 of mold 900 at an angle.

Flattened edge 1206 of dilation element 1205 has greater surface areathan the unflattened edge of corresponding structural feature 320 (FIG.3), which is shown to have a bead-like shape. The edge 1206 may bemaintained in a shape having smaller surface area to enhance thefocusing of the pressure transmitted from edge 1206 to a stenosed vesselwall. Various techniques may be utilized to prevent edge 1206 ofstructural feature 320 from flattening when contacting an inner surfaceof the mold 900. For example, FIG. 15 shows a jacket 1500 which may beplaced over the structural feature 320 of the parison 300 before blowmolding the parison 300. The jacket 1500 shields the structural feature320 from the inner surface of the wall 901 of the mold 900 during radialexpansion of parison 300 within the mold 900, thereby maintaining theshape of the structural feature 320. The jacket 1500 may be a pre-formedmolding that is formed from a material that has a higher melttemperature than the temperature used during blow molding. Examples ofsuitable materials for the jacket 1500 include PEEK, PTFE, and otherrelatively high-melt temperature materials. Because the jacket 1500 hasa higher melt temperature than the temperatures utilized during blowmolding, the shape of the jacket 1500 may be maintained. The material ofthe jacket 1500 may also be sufficiently heat resistant (e.g., KEVLAR®)to prevent heat transfer from the exterior of the mold into the interiorregion of the mold. As a result of the heat resistant properties of thejacket 1500 material, the structural feature 320 may be prevented frombeing heated to its melt temperature.

A perspective view of the jacket 1500 is shown in FIG. 17. Thelongitudinal length of the jacket 1500 may be sufficient to span theentire length of each of the structural features 320 of the parison 300.Screws, clips, adhesives or other joining methods known to one ofordinary skill in the art may be used to secure the jacket 1500 aroundits respective structural feature 320.

Alternatively, the jacket 1500 may be designed to snap fit over itsrespective structural feature 320. A snap fitted jacket 1500 may flexlike a spring, usually over a designed-in interference, and return toits original position to create the desired snap assembly between two ormore parts. The snap-fit assembly of the jacket 1500 and its structuralfeature 320 may be designed to have adequate holding power withoutexceeding the elastic or fatigue limits of either material. FIG. 18shows a longitudinal cross-sectional view of a single jacket 1500disposed over the region of the parison 300 containing structuralfeatures 320 within mold 900. As the jacket 1500 and parison 300radially expand during blow molding, as indicated by the arrows in FIG.18, the jacket 1500 protects the structural features 320 from flatteningupon contacting wall 901 of mold 900. After the blow molding iscompleted, the snap-fitted jacket 1500 may be released from itsstructural feature 320 with an appropriate tool. The snap-fitted jacket1500 may be designed for easy release and re-assembly over multipleblow-molding cycles.

As shown in FIG. 15, multiple jackets 1500 may be used to cover all ofthe features. Alternatively, one or more jackets 1500 may be used tocover less than all of the features.

Other means may be utilized to prevent edge 1206 of structural feature320 from flattening when contacting an inner surface of the mold 900during blow molding of the parison 300. For example, a second mold maybe used to reshape the dilation elements 130 (FIGS. 1, 3, 4) into theoriginally shaped structural features 320 as well as realign thedilation elements 130 along the longitudinal direction of the balloon150 (FIG. 1). The second mold may possess multiple grooves into whicheach of the dilation elements 130 insert thereinto. The entire parison300 may be inserted into the second mold. Alternatively, only structuralfeatures 320 may be inserted into the second mold, and the body portionof the parison 300 remains outside of the second mold. Alternatively,the original mold used in the blow molding process may contain multiplegrooves into which the structural features 530 can expand. Thestructural features 530 conform to the shape of the grooves to form theresultant dilation elements 1205. Other means as known in the art forpreserving the desired bead shape are contemplated.

Preferably, the resultant balloon 150 that is formed after the blowmolding process described in FIGS. 9-11 comprises dilation elements 130(FIGS. 1, 3, 4) and connector 120. Because the extension elements 330(FIG. 3) undergoes stress-induced plastic deformation during the blowmolding process, the structural integrity of the resultant dilationelements 130 is maintained such that they do not become part of the wallof the body portion 310. As a result, upon inflation of the balloon 150,the dilation elements 130 remain structurally intact to focus the forceat their respective points of contact with a stenosed vessel wall.Because FIGS. 1, 3, and 4 show that the dilation elements 130 areintegrally part of the parison 300 (i.e., raw balloon tubing), secondaryprocesses are not required for attachment to the outer surface 140 ofthe balloon 150.

The resultant balloon 150 preferably comprises dilation elements 130which are circular-shaped, as shown in FIGS. 3 and 4. Other shapes arecontemplated. For example, a dilation element 1320 which is offset froma central radial plane through the connector is another possible design.

The resultant balloon 150 is preferably folded into a pleatedconfiguration of small diameter for delivery to a target stenosed vesselsite. The pleats are initially formed during delivery of the balloon 150and may be reformed upon deflating the balloon 150 from the inflatedstate. FIG. 19 shows the balloon 150 in a deflated state having apleated arrangement with the dilation element 130 and connector 120disposed along the top of each of the pleats 1901, 1902, 1903, and 1904.Upon delivery and deflation from the inflated state, the balloon 150transforms into the pleated arrangement. Four pleats 1901, 1902, 1903,and 1904 are shown positioned circumferentially about a central axis ofthe balloon 150. Less than four pleats or greater than four pleats maybe utilized depending, in part, upon the profile of the balloon 150required for a particular application. The pleats 1901, 1902, 1903, and1904 may be wrapped about a central axis of the balloon 150 to form thepleated arrangement, thereby creating a sufficiently low profile of theballoon 150 during delivery to and removal from the target site.

The dilation elements 130 and their respective connectors 120 are shownpreferably extending from the top of the pleats 1901, 1902, 1903, and1904. The presence of the dilation elements 130 and their respectiveconnectors 120 disposed along the top of the pleats 1901-1904 mayfacilitate the ability of the inflated balloon 150 to refold into thepleated configuration of FIG. 19. When the balloon 150 is deflated, theballoon 150 material between pleats 1901-1904 may have a higher tendencyto collapse than the pleated region of the balloon 150 material. Inother words, the balloon 150 material between the pleats 1901-1904 hasless resistance to collapsing into the pleated arrangement than thepleated region. The pleated region has a greater wall thickness andtherefore possesses relatively greater rigidity as a result of at leasta portion of the extension element 330 of the parison 300 absorbing intothe wall during radial expansion of the parison 300 within the mold 900.

Alternatively, the pleats 1901, 1902, 1903, and 1904 may be configuredsuch that the dilation elements 130 are disposed between adjacent pleats1901, 1902, 1903, and 1904.

The ability to reform the pleated configuration may prevent theundesirable phenomenon known in the art as “winging” from occurring.Winging refers to flattening of the balloon 150 into a wing-likestructure characterized by an absence of folds along the balloon 150.Because there are no folds, the profile of the balloon 150 may becomerelatively wide such that removal and reentry of the balloon 150 withinan outer sheath potentially becomes difficult. Thus, the pleats1901-1904 may substantially eliminate the winging problem.

The balloon 150 may be formed from any suitable polymeric material knownto those of ordinary skill in the art, including polyethyleneterephthalate (PET) and nylon. In one preferred embodiment, the materialis Grilamid® L25, which is a specific nylon-12 material known in theart. Alternatively, the balloon 150 may be formed from a first polymericmaterial and the protuberance 110 may be formed from a second polymericmaterial.

In one particular embodiment, the balloon 150 and protuberance 110 maybe coextruded from two different materials. The balloon 150 may beextruded from a conventional first polymeric material (e.g., nylon), thedilation element 130 may be extruded from a second polymeric materialmore rigid than the first polymeric material, and the connector 120 maybe extruded from a blend of the first and the second polymericmaterials. A transition point from the first polymeric material to thesecond polymeric material preferably occurs along the connector 120. Inparticular, it is preferable that a lower portion of the connector 120(i.e., from the predetermined transition point along the connector 120downwards to the interface of the connector 120 and the outer surface140 of the balloon 150) may be formed from the same first polymericmaterial as the outer surface 140 of the balloon 150 to enable thislower portion of the connector 120 to become absorbed into the wall ofthe balloon 150 during the blow molding process. The first polymericmaterial may be relatively softer and more compliant than the secondpolymeric material, thereby enabling longitudinal and radial stretchingduring blow molding. The lower portion of the connector 120 may beadequately sized such that there is a sufficient amount of firstpolymeric material that absorbs into the wall of the balloon 150 withoutsubstantial absorption of the upper portion of the connector 120 (i.e.,from the predetermined transition point along the connector 120 upwardsto the dilation element 130) into the wall of the balloon 150. The upperportion of the connector 120 is connected to the dilation element 130.The dilation element 130 contacts the stenosed vessel wall.

The blending of a first polymeric and a second polymeric material may beachieved by several different types of coextrusion processes. Oneparticular screw extrusion process is shown in the block diagram of FIG.20. FIG. 20 shows that the relatively softer first polymeric material #1is extruded in screw extruder #1 and the relatively more rigid secondpolymeric material #2 is extruded in screw extruder #2, as shown inrespective steps 10 and 20. Each of the materials is melted andpressurized in their respective extruders #1 and #2 (respective steps 10and 20). Each screw extruder #1 and #2 provides discrete flow channelsthrough which materials #1 and #2 flow therewith in. Screw extruder #1may feed into a supply tube #1 within a common feed block (step 30), andscrew extruder #2 may feed into a supply tube #2 within the common feedblock (step 40). Each supply tube may thereafter branch off intomultiple flow channels located internally of the feed block. The flowchannels enable material #1 to enter specific portions of the parisonmold in step 50 to form the body portion 310 of the parison 300 (FIG.3). Another group of flow channels enable material #2 to feed into thatportion of the parison mold which forms the structural feature 320 ofthe parison 300 (step 60). Yet another group of flow channels convergeinto a single flow channel and thereafter feed into that portion of theparison mold along the extension element 330 of the parison 300, so asto form extension element 330 and also allow mixing of material #1 andmaterial #2 at a transition point located along the extension element330 of the parison 300 (step 70). The feed block may be designed suchthat mixing of material #1 and #2 may occur simultaneously with theshaping of the extension element 330.

Materials #1 and #2 are preferably selected such that there iscompatibility in at least two ways. First, selection of suitablematerials #1 and #2 may require that both materials #1 and #2 have acommon processing temperature range. In other words, the materials #1and #2 have a common temperature range such that both materials #1 and#2 can be processed within the common temperature range without thermaldegradation of one of the materials. Second, selection of suitablematerials #1 and #2 is such that they have an affinity for each other sowhen combined into the flow channels of the feed block, a naturalchemical bond is formed between the materials which assures thatmaterials #1 and #2 do not separate upon incurring a load duringsubsequent blow molding of the parison 300 into the balloon 150. Amodification step to one or both of the materials #1 or #2 may becarried out prior to step 70 to functionalize the materials #1 or #2 sothat they are chemically compatible with each other, thereby forming achemical bond.

The extrudate from steps 50 and 60 and the coextrudate from step 70 arecooled in cooling troughs, as shown in step 80. The cooling troughs coolmaterial and solidify the extrudate into the desired shape of theparison 300. The net result is a coextruded parison in which the bodyportion 310 and a lower portion of the extension element 320 are formedfrom softer, compliant material #1 and an upper portion of the extensionelement 330 and structural feature 320 is formed from relatively morerigid, less compliant material #2. Other means for blending twodifferent materials to form a monolithic (i.e., unitary) extrudateparison structure as known to one of ordinary skill in the art are alsocontemplated.

In an alternative embodiment, the cylindrical portion of the parison andthe extension element-structure feature may not be a monolithicstructure but rather may be separately extruded structures. Furthermore,the cylindrical portion of the parison may be formed from a firstpolymeric material and the extension element-structure feature may beformed from a blend of the first and the second polymeric materials, asdescribed above. The cylindrical portion of the parison and theextension element-structure feature may be separately extruded andsubsequently attached to each other. Various means may be utilized forconnecting the lower portion or base of the extension element to thecylindrical portion of the parison, including a thermal bond. Onepreferred type of thermal bond could involve laser welding the base ofthe extension element to the cylindrical portion of the parison. Thelaser weld enables pinpointing high heat in a localized area (i.e., atthe interface of the connector and the outer surface of the balloon)without adversely impacting the balance of the cylindrical portion ofthe parison and the structural feature. Alternatively, a chemical bondsuch as an adhesive bond may be used to attach the base of the extensionelement to the cylindrical portion of the parison. The particularconnecting means may be dependent upon the materials of the parison,extension element, and structural feature.

While preferred embodiments of the invention have been described, itshould be understood that the invention is not so limited, andmodifications may be made without departing from the invention. Thescope of the invention is defined by the appended claims, and alldevices that come within the meaning of the claims, either literally orby equivalence, are intended to be embraced therein. Furthermore, theadvantages described above are not necessarily the only advantages ofthe invention, and it is not necessarily expected that all of thedescribed advantages will be achieved with every embodiment of theinvention.

What is claimed is:
 1. A balloon catheter for dilation of a vessel wall,comprising: a balloon having a distal neck portion at a distal end, adistal tapered portion proximally adjacent to the distal neck portion, aproximal tapered portion, and a proximal neck portion at a proximal endand proximally adjacent to the distal neck portion proximal taperedportion, wherein at least a length of an outer surface of the ballooncomprises a working diameter between the distal tapered portion and theproximal tapered portion; a protuberance continuously extending from theproximal neck portion along the tapered proximal portion, along theouter surface of the working diameter, and along the tapered distalportion to the distal neck portion, the protuberance monolithicallyformed with the balloon at an interface region, the protuberancecomprising a dilation element and a connector, the dilation elementextending away from the outer surface of the balloon and defined by asecond effective width, the connector connecting the dilation element tothe outer surface of the balloon at the interface region, the connectordefined by a first effective width less than the second effective widthof the dilation element, wherein the dilation element has a flattenedouter surface along at least the proximal and distal neck portions. 2.The balloon catheter of claim 1, wherein the dilation element has aflattened outer surface along the proximal and distal tapered portions.3. The balloon catheter of claim 1, wherein the dilation element has anunflattened outer surface along at least a portion of the workingdiameter.
 4. The balloon catheter of claim 1, wherein the protuberanceextends along the entire length of the balloon and the dilation elementhas a rounded outer surface along the working diameter and a flattenedouter surface along the proximal and distal neck portions and along theproximal and distal tapered portions.
 5. The balloon catheter of claim1, wherein the connector having the second effective width consists ofthe same material as the balloon and as the dilation element having thefirst effective width.
 6. The balloon catheter of claim 1, wherein theballoon and the protuberances form a monolithic structure manufacturedfrom an extruded parison by blow-molding.
 7. The balloon catheter ofclaim 1, wherein the outer surface of the balloon in a deflated statecomprises a plurality of pleats wrapped about an axis of the balloon. 8.The balloon catheter of claim 7, wherein the protuberance is presentmultiple times, forming multiple protuberances, and wherein one of themultiple protuberances is disposed along the top of each of the pleats.9. The balloon catheter of claim 8, wherein the interface region has awall thickness greater than a wall thickness of a noninterface regiondisposed along another portion of the outer surface of the balloon. 10.The balloon catheter of claim 1, wherein the dilation element hasstraight edges inwardly tapered toward an outer edge of the dilationelement along the working diameter.
 11. The balloon catheter of claim 1,wherein the balloon, connector and dilation element comprise one or morepolymeric materials.
 12. The balloon catheter of claim 11, wherein theballoon, connector and dilation element comprise nylon.
 13. The ballooncatheter of claim 1, wherein the balloon, connector and dilation elementcomprise one or more polymeric materials, the interface region has awall thickness greater than a wall thickness of a noninterface regiondisposed along another portion of the outer surface of the balloon, theouter surface of the balloon in a deflated state comprises a pluralityof pleats wrapped about an axis of the balloon, and the dilation elementhas a flattened outer edge along the proximal and distal taperedportions.
 14. The balloon catheter of claim 1, further comprising ashaft having a distal end and a proximal end, the balloon being mountedon the distal end of the shaft at the proximal neck portion and at thedistal neck portion, wherein the shaft further comprises an inflationlumen extending therethrough in fluid communication with an interiorregion of the balloon, the balloon thereby being expandable between adeflated state and an inflated state.